This invention relates to methods of making silicon solar cells and other silicon photovoltaic cells.
For making silicon photovoltaic cells, particularly solar cells, a great number of process steps has heretofore been required and which necessarily involves considerable manufacturing expense. First, a suitable silicon wafer had to be subjected to a diffusion for forming a PN junction; then, an antireflective layer had to be provided either through surface sputtering or vapor deposition of specific layers for subsequently carrying out the electrode metallization, one of said layers being finally designed as a comb-shaped electrode in a conventional manner.
The absorption capacity and consequently the efficiency of solar cells made in this manner can be considerably improved if, as previously described in German Offenlegungsschrift No. 1 621 511, the irradiated surface is coated with a fine matrix of silicon pyramids. This can be produced by etching a silicon monocrystal surface in (100) orientation so that after this etching process silicon pyramids with their (111) edges remain on the surface.
It is disadvantageous that the PN junction has to be made subsequently, and that the raw material, i.e., the silicon monocrystal layer is relatively expensive. Even if non-monocrystalline silicon can be substituted, (since polycrystalline silicon cannot be used at all), there remains the problem that the manufacture of this material is complex and relatively difficult.
Although the use of polycrystalline and amorphous silicon for solar cells is known per se, the application of electrodes and the application of antireflective coating, particularly for generating a planar PN junction, represent considerable difficulties. A summary on solar cells of conventional design is given in the periodical "Umschau", Volume 77 (1977), No. 13, entitled "Elektrische Energie von der Sonne", pp. 421 to 427.